Corona discharging device for electrophotographic process

ABSTRACT

Apparatus for use in imparting charge to a member including a conductive element having an end juxtaposed with the surface of the member being charged and a needle-form corona discharge electrode providing a discharge directed principally onto the conductive element. The corona discharge electrode is disposed in a plane substantially nonperpendicular to the member being charged and intersecting the plane containing the conductive element.

United States Patent inventors Hiroshi Tanaka;

. Masaydshi lshihara, both of Tokyo, Japan Appl. No. 744,117 Filed July11, 1968 Patented May 25, 1971 Assignee Canon Camera Kabashiki KaishaTokyo, Japan Priority July 14, 1967 Japan CORONA DISCHARGING DEVICE FORELECTROPHOTOGRAPHIC PROCESS 8 Claims, 10 Drawing Figs.

US. Cl 317/4, 317/262, 250/49.5 Int. Cl 1105b 1/00 [50] Field of Search317/4, 262; 250/495 (60), 49.5 (61) [56] References Cited UNITED STATESPATENTS 3,133,193 5/1964 Guillotte et a1. 317/262X 3,303,401 2/1967Naumann et a1 250/49.5(61) Primary Examiner-Lee T. Hix Attorney-Watson,Leavenworth & Kelton ABSTRACT: Apparatus for use in imparting charge toa member including a conductive element having an end juxtaposed withthe surface of the member being charged and a needle-form coronadischarge electrode providing a discharge directed principally onto theconductive element. The corona discharge electrode is disposed in aplane substantially nonperpendicular to the member being charged andintersecting the plane containing the conductive element.

CORONA DISCHARGING DEVICE FOR ELECTROPHOTOGRAPHIC PROCESS This inventionrelates to improvements in corona dischargers for electrophotographicuse.

Conventional discharge electrodes of corona dischargers for chargingphotosensitive members in electrophotography include fine metal wiressuch as tungsten filaments, or needleform electrodes. In the formercase, the metal wire is, in general, as fine as from 6/100 to 8/100 mm.in diameter, and is frequently broken during handling or in usewhereupon the high-voltage output may be short circuited, destroying theelectric source, or a dangerous condition may occur.

In the latter case, the end of the needle-form electrode is directedtoward the photosensitive member surface, and the electrostatic field isof high intensity in the vicinity of the needle end. As a result, on thesurface of the negative needle-form electrode secondary electrondischarge by positive ion is predominant while travel of singleelectrons caused only by negative ions is inhibited. Thus, a plasmastate is inevitably formed inwhich positive charge and negative chargeare present in a mixed state. Electrostatic charge of polarity oppositeto that'of the electrode is thus concentrated on the photosensitivemember surface and the possibility of generating a locally highdielectric field is increased, and thereby corona discharge sometimesevolves into a spark discharge or streamer. Accordingly, thephotosensitive member may be damaged or such excess current may flow asto destroy the high-voltage electric source. Even if spark dischargedoes not occur, there are the disadvantages that uniform development isnot obtained, and that half-tone is not obtained.

An object of this invention is to overcome the abovedescribeddisadvantages in a corona discharger employing needle-form electrodes.In accordance with this invention, the ends of the needle-formelectrodes are directed not toward the photosensitive member, but towardthe shield member or shield plate.

The term needle-fon'n electrode" as used throughout the specificationand the appended claims is intended to mean an electrode in the form ofa projected member having an elongated body tapering to a coronadischarge point, such as, for example, needle, sawtooth, cone and thelike.

In accordance with the invention, the main discharge is carried outbetween the needle-form electrode and the shield member in a directionalmost parallel to the photosensitive surface, and therefore the localelectric field is directed towards the shield member. In other words, acorona of polarity opposite to that of the needle-form electrode, i.e.the locally strong corona, is directed to the shield member so that thecircumferential electric field of the main discharge acts on the surfaceof the photosensitive member. Thereby, a uniform and soft electric fieldis applied to the photosensitive member surface, the charged zone iswidened, and remarkably excellent charging can be carried out. The termcircumferential" refers not only to the outer portion of the electricfield, but also to portions thereof exclusive of the central portion ofthe main discharge in the electric field.

In furtheraccordance with this invention, a plurality of needIe-formelectrodes are commonly supported by a conductor, with the needle-formelectrodes alternately arranged to discharge in respectively oppositedirections. lrregularity in amount of charge deposited on thephotosensitive member surface is thus prevented.

It is an object'of this invention to provide an improved coronadischarger having needle-form electrodes for electrophotographic use.

It is another object of this invention to provide a corona dischargerhaving needle-form electrodes which provides a uniform, wide and softelectric field on a photosensitive member surface.

It is a further object of this invention to provide a corona dischargerhaving needle-form electrodes which facilitates the formation ofhalf-tone image.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is had to the following detaileddescription thereof to be read in conjunction with the accompanyingdrawings, wherein:

FIG. I is a diagram showing a first state of discharging of a coronadischarger of this invention;

FIG. 2 is a diagram showing a subsequent state of the charging operationofa corona discharger of this invention;

FIG. 3 is a schematic diagram of an embodiment of a corona dischargeraccording to this invention;

FIG. 4 is a diagram showing an arrangement of needle-form electrodes ofthis invention;

FIG. 5 is a front view of an embodiment of this invention whereneedle-form electrodes are provided on a-supporting conductive rod;

FIG. 6 shows an outline of various kinds of charging devices inaccordance with the invention;

FIG. 7 is a schematic diagram explaining the principle of an aspect ofthis invention;

FIGS. 8 and 9 are schematic drawings of embodiments of this invention;

FIG. 10 shows a sawtooth-type electrode.

Referring to FIG. I, l is a needle-form electrode; 2 is a shield plateor shield wire; 3 is a photosensitive member.

When direct current voltage is applied to needle-form electrode 1,electric field F is generated from the end of needleform electrode 1toward shield plate 2, and photosensitive member 3 is charged bycircumferential electric field Fx in the primary stage of chargingoperation as is shown in FIG. I. In the latter stage of the chargingoperation the photosensitive surface bears charge and electric field Fxis eliminated as is shown in FIG. 2.

When electrodes I and I, are directed in the respectively oppositedirections from a common or discontinuous electrode supporting conductor4 as is shown in FIG. 3, irregularity in charging of photosensitivesurface 1 is effectively eliminated. For this purpose electrodes I and 1are arranged as shown in FIG. 4.

As an alternate manner in which the needle-form electrodes may beprovided, a hole or groove 5 is formed in supporting conductor 4 in aslant direction as is shown in FIG. 5, and one electrode is inserted toform the two electrodes l, and 1,. The end of the needle may be shapedin conical form or in the form of knife edge.

The needle-form electrode may be arranged in such a way that itsdirection, i.e., the direction of the axis of its elongated body, is atan angle 0 with the photosensitive surface as shown by 1, in FIG. 3. Itis preferableto adjust the angle 0 from 20 to 40, preferably about 30.

This invention may be applied to various kinds of charging devices. Incase of single corona dischargers shown in FIG. 6, a to c, remarkablyexcellent electrostatic charging is obtained when a copper wire of 1 mm.in diameter is used as needleform electrode 1, aluminum plate is used asshield plate 2, the distance between the end of the needle and theshield plate is from 8 to 10 mm., the interval between the needle-formelectrodes is 20 mm., and the distance between the end of theneedle-form electrode and the photosensitive surface is about 12 mm.,high voltage of 2.5 kv. is applied to the electrode supportingconductor, and high voltage of 2.5 kv. is applied to the shield plate.

According to'another aspect of this invention, the needleform electrodeis particularly arranged in such a manner that the extension of the axisof the electrode elongated body crosses the material to be charged at anacute angle, preferably an angle ranging from 20 to 40and the end of theshield member positioned nearest the material to be charged liessubstantially on the extension of the axis of the electrode elongatedbody.

Referring to FIG. 7, needle-form electrode 4 is placed in such a mannerthat the extension of axis X of the electrode elongated body crossesshield plate 2 at edge 2' of shield plate 2 and crosses the material tobe charged, for example, a

photosensitive plate P at an angle a. When the end of the electrode isin edgelike form, corona is easily generated.

Referring to the upper half of FIG. 8 and-to FIG. 9, electrode baseplate 3 is mounted on support 6 in a housing of the charging device, end2' or 2, facing photosensitive plate P of shield plate 2 or2,substantially lies on the extension of the axis of the electrode, andsuch extension of the axis of the elongated body of electrode 4 or 4,crosses photosensitive plate P at an angle a ranging fromabout 20 to 40when the shield plate 2 or 2, is positioned in such a manner that it isat right angle with photosensitive plate P. When the device is soarranged, the plasma having disadvantageous effects, as mentioned above,and ions existing in the vicinity thereof are attracted onto shieldplate 2 or 2,and only the ion group existing around the above-mentionedions has an effect on photosensitive plate P to enhance the chargingefficiency.

FIG. 8 also shows a structure in which thedevice of this invention isused as a double corona discharger. Needle-form electrodes 4 and 4, areprovided with respectively different polarities and are of sawtoothtype. Sawtooth electrodes 4 and 4, are integrally formed on the bothsides of base plate 3 (e.g. as shown in FIG. 10). In the abovestructure, the following dimensions result in an excellent charging:

a angle between the axis of the electrode elongated body and the surfaceof P=30 a distance between the pointed end of the electrode and theshield plate 12 mm.

b distance between the pointed ends of electrodes of different polarity14 mm.

c distance between the pointed ends of electrodes of the same polarity 5mm.

Referring again to FIG. 9, shield plate 2, is placed at the center, andneedle-form electrodes 4 and 4, are symmetrically placed on both side ofthe shield plate. Each of needle-form electrodes 4 and 4, are arrangedat only one side of each base plate 3.

Referring to FIG. 10, the sawtooth-type electrode consists of base plate3 and sawteeth 4. The sawteeth on both sides are alternately projected.This type of sawtooth electrode plate can be easily made by using apress, and therefore they can be obtained at low cost with high accuracyof dimensions by mass production.

The corona charging devices of this invention are free fromdisadvantages, such as breaking of wire and short circuit oftenoccurring in conventional fine charging wire coronas. There is no fearof irregular charging and an excellent halftone can be obtained sincelocally strong charging is not involved. Furthermore, there are suchadvantages that the charging efficiency is high, the capacity requiredof high-voltage electric sources is low, dielectric breakdown of thephotosensitive member is avoided and durability of the charging deviceis improved.

We claim: a

1. Apparatus for use in imparting charge to the surface of a chargeablemember comprising a conductive element having an end juxtaposed withsaid chargeable member surface, and an electrode providing coronadischarge directed onto both said conductive element and said chargeablemember surface and comprising an elongated body tapering to a coronadischarge point, the longitudinal axis of said electrode body bothintersecting a plane containing said conductive element and forming anacute angle with a plane containing said chargeable member surface.

2. The apparatus claimed in claim 1 wherein said electrode bodylongitudinal axis intersects said plane containing said conductiveelement substantially perpendicularly.

3. The apparatus claimed in claim 1 wherein said longitudinal axis ofsaid electrode body intersects said plane containing said conductiveelement substantially at said conductive element end.

4. The apparatus claimed in claim 1 including in addition a conductorsupporting said electrode, a further electrode supported by saidconductor and comprising an elongated body tapering to a coronadischargepoint, and a further conductive element disposed on an oppositeside of said support conductor from said first-mentioned conductiveelement and having an end juxtaposed with said surface, said furtherelectrode providing corona discharge directed onto both said furtherconductive element and said member surface, the longitudinal axis ofsaid second electrode body both intersecting a plane containing saidfurther conductive element and forming an acute angle with said planecontaining said chargeable member surface.

5. The apparatus claimed in claim 4 wherein said electrode and furtherelectrode comprise sawteeth formed integrally with said supportconductor.

6. The apparatus claimed in claim 4 wherein said electrode and furtherelectrode comprise portions of a single electrode member supported in atransverse aperture in said support conductor.

7. The apparatus claimed in claim 1 including a further electrodedisposed on an opposite side of said conductive element from saidfirst-mentioned electrode and providing corona discharge onto both saidconductive element and said member surface, said further electrodecomprising an elongated body tapering to a corona discharge point, thelongitudinal axis of said further electrode body both intersecting aplane containing said conductive element and forming an acute angle offrom 0 to 40 with said plane containing said chargeable member surface.

8. The apparatus claimed in claim 4 wherein said electrode and furtherelectrode are displaced from one another along said support conductor.

UNITED STATES l.A'llflN'l owner: (I I EH! E ICATE 01* (10 RR EU! I ()NPatent No. 3 581 149 Dated May 25 1971 Inventor(s) Hiroshi Tanaka et a1.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby' corrected as shown below:

Item [73] Title page, "Canon Camera Kabashiki Keisha" should read -CanonKabushiki Kaisha-.

Signed and sealed this 9th day of November 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer ActingCommissioner of Patents USCOMM-DC 603764 69 u s. GDVIRNMEIT rnmnm; orncrum 0-156- n4 F ORM PO-1050(10-69)

1. Apparatus for use in imparting charge to the surface of a chargeablemember comprising a conductive element having an end juxtaposed withsaid chargeable member surface, and an electrode providing coronadischarge directed onto both said conductive element and said chargeablemember surface and comprising an elongated body tapering to a coronadischarge point, the longitudinal axis of said electrode body bothintersecting a plane containing said conductive element and forming anacute angle with a plane containing said chargeable member surface. 2.The apparatus claimed in claim 1 wherein said electrode bodylongitudinal axis intersects said plane containing said conductiveelement substantially perpendicularly.
 3. The apparatus claimed in claim1 wherein said longitudinal axis of said electrode body intersects saidplane containing said conductive element substantially at saidconductive element end.
 4. The apparatus claimed in claim 1 including inaddition a conductor supporting said electrode, a further electrodesupported by said conductor and comprising an elongated body tapering toa corona discharge point, and a further conductive element disposed onan opposite side of said support conductor from said first-mentionedconductive element and having an end juxtaposed with said surface, saidfurther electrode providing corona discharge directed onto both saidfurther conductive element and said member surface, the longitudinalaxis of said second electrode body both intersecting a plane containingsaid further conductive element and forming an acute angle with saidplane containing said chargeable member surface.
 5. The apparatusclaimed in claim 4 wherein said electrode and further electrode comprisesawteeth formed integrally with said support conductor.
 6. The apparatusclaimed in claim 4 wherein said electrode and further electrode compriseportions of a single electrode member supported in a transverse aperturein said support conductor.
 7. The apparatus claimed in claim 1 includinga further electrode disposed on an opposite side of said conductiveelement from said first-mentioned electrode and providing coronadischarge onto both said conductive element and said member surface,said further electrode comprising an elongated body tapering to a coronadischarge point, the longitudinal axis of said further electrode bodyboth intersecting a plane containing said conductive element and formingan acute angle of from 0* to 40* with said plane containing saidchargeable member surface.
 8. The apparatus claimed in claim 4 whereinsaid electrode and further electrode are displaced from one anotheralong said support conductor.